How to Use Optional with findBy Methods:

Spring Data MongoDB repositories support the use of java.util.Optional as a return type for findBy methods. This provides a robust way to handle cases where a matching document might not be found, preventing NullPointerExceptions and promoting clearer code.

How to Use Optional with findBy Methods:

• Define the Repository Method: Declare your findBy method in your Spring Data MongoDB repository interface with Optional<YourEntityType> as the return type.

Java

    import java.util.Optional;
    import org.springframework.data.mongodb.repository.MongoRepository;
    
    public interface UserRepository extends MongoRepository<User, String> {
        Optional<User> findByEmail(String email);
        Optional<User> findById(String id); // findById already returns Optional by default
    }

• Consume the Optional Result: When calling these methods, you will receive an Optional object. You can then use the various methods provided by Optional to handle the presence or absence of a user.

Java

    import java.util.Optional;
    
    public class UserService {
        private final UserRepository userRepository;
    
        public UserService(UserRepository userRepository) {
            this.userRepository = userRepository;
        }
    
        public User getUserByEmail(String email) {
            Optional<User> userOptional = userRepository.findByEmail(email);
    
            // Option 1: Check for presence and act accordingly
            if (userOptional.isPresent()) {
                return userOptional.get(); // Get the User object
            } else {
                // Handle case where user is not found
                throw new UserNotFoundException("User with email " + email + " not found.");
            }
    
            // Option 2: Use orElse() to provide a default value
            // return userOptional.orElse(new User("default@example.com")); 
    
            // Option 3: Use orElseThrow() to throw a specific exception if not present
            // return userOptional.orElseThrow(() -> new UserNotFoundException("User with email " + email + " not found."));
        }
    }

Benefits of Using Optional:

• Explicit Null Handling: 

  Forces you to explicitly consider the possibility of a null result, reducing the likelihood of NullPointerExceptions.
• Improved Readability: 

  Makes the code's intent clearer, as the return type itself indicates that the value might be absent.
• Functional Programming Style: 

  Integrates well with functional programming constructs available in Java 8 and later.